Dynamo-electric machine



Oct. 9, 1934. GR|FF|TH$ 1,976,554

'DYNAMO ELECTRIC MACHINE Filed April 7, 1935 lnventorw Leonard. Griffi thS.

His Attorney.

Patented Oct- 9, 1934 PATENT. OFFICE.

1,976,554 I DYNAMO-ELECTRIOMACHINE Leonard Grifilths, Coventry, England, assignor to General Electric Company, a corporation of New York Application April 7, 1933, Serial No. 664,985 In Great Britain April 8, 1932 4 Claims; (Cl. 171209) My invention relates to dynamo-electric machines and more particularly to such machines for supplying current to the-ignition systems of internal combustion engines.

Dynamo-electric machines of the inductor alternator type are used extensively to supply the ignition systems of internal combustion engines, because they provide a construction having low inertia of the rotating parts. In certain applications of internal combustion engines, such as in aircraft propulsion, the engine is often accelcreated to high speed at'an extremely rapid rate and the inertia effect of the rotating parts of the ignition generator, or magneto, produces excesslve strain in the transmission mechanism connecting it to the engine shaft. Frequently the generator drive mechanism is broken because of this strain, and for this reason it is highly important. that the rotating member of the generator should have low inertia.

It isan object of my invention to provide a dynamo-electric machine having a low inertia rotatable member which shall ,be of a simple and rugged construction. I

Another object of my invention is to provide a rotatable member fordynamo-electric machines of the inductor alternator type which shall be capable of resisting the high centrifugal forces.

A further object of my invention is to provide a rotatable member for dynamo-electric machines of the inductor alternator type of high efIiciency having a rotating permanent magnet structure, which can be easily assembled. .Further objects and advantages of myinvention will appear as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification. H

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 is a longitudinal sectional view of a magneto constructed in accordance with my invention; Fig. 2- is a view of the magneto shown in Fig. 1 on the line 2--2 of Fig. 1; Fig.'3

is a side elevational view partlyin section of a modified form of rotor embodying my invention;

. and Fig.4 is a transverse section on the line 4-9-4 rotatablemember. 11 mounted for rotation within the stationary member. The stationary member 10 comprises a U-shaped laminated core 12 having a winding 13 arranged on the core at the top thereof and connected to the output circuit in the usual manner. The lower endsof the core. 12 are provided with cylindrical faces 14 and 15,

which surround the rotatable member 11. The

rotatable member 11 comprises .a non-magnetic shaft 16 of non-magnetic steel, or other suitable material, about which are secured a plurality of permanently and highly magnetized bars 17 and- 17a of cobalt steel or the like, which are arranged longitudinally of the shaft 16 In order to sup port the bars 1'? and 17a on the shaft I provide a plate 18 of mild steel, or similar magnetic materialnear one end of the shaft and at right angles thereto, and near the other end I provide a plate 19 of brass or similar non-magnetic material. The magnetized bars 17 and 17a are provided with mainportions'ZO of substantially rectangular cross-section and with reduced round portions 21 and 22, The reduced portions 21 and a 22 are fitted into recesses 18a. and 19a in the plates 18 and 19, respectively. The reduced portions 22 extend from the plate 19 to approximately the middle of the bars 1'7 and 17a and terminate in shoulders 23 -on the bars. In Figs. 1 and 2 I have shown the rotatable member 11 as having two groups of three bars each, one group consisting of the bars 1'7, and the other group consisting of the bars 17a.- The groups of bars are arranged so that the ends of all bars of the group consisting of bars 17 adjacent the nonmagnetic plate 19 are of one polarity, while the ends of all bars of the other group-consisting of bars 170 adjacent this plate 19 are of the opposite polarity. Themagnetic plate 18 and thegroups of bars 17 and 17a then form a horse-shoe magnet, which I provides a two-pole rotor for the magneto. Lam- -inated pole-pieces 24 are provided with openings 24a fitted on the. reduced portions 22 of each is provided to reinforce the bars against the bend ing effect of centrifugal force near their midportions. The laminations of these pole pieces have arcuate edges, which conform to the cylindrical faces 14 and 15 of the stationary member to provide the desired air gap, and the arcuate edges of the laminations are of such extent-as to produce the desired wave-form of alternating flux in the stationary member upon rotation of the rotatable member. s

In assembling the rotatable member shown-in. Figs. 1 and 2, I first secure the plate lB rigidly to the shaftl'G/then insert the bars 17 and 17a in the openings 18a in the plate 18, place the nonmagnetic disc 25 in position against the shoulders 23, arrange the laminated pole-pieces on the bars against the ,disc 25, then place the plate 19 in position and compress the laminations tightly between the plate 19 and the disc 25. When plate '19 is in position I secure it firmly to the shaft and in this manner insure a rigid assembly of the rotatable member --11.

In the operation'of the magneto shown in Figs. 1 and 2 when the rotatable member 11 is rotated, the pole-pieces 24 set up a varying flux in the core 12 of the stator 10, and an alternating voltage is induced in the winding 13. The rotatable member 11 is of a construction such that it may he rotated at high speed without liability of seri-- ous deformation or unbalance due to centrifugal force. Because of the arrangement of the magnetic bars 17 and 17a longitudinally along the tion. This rotatable member comprises a nonmagnetic shaft 26, magnetic end plate 27 secured at one end of the shaft, and a non-magnetic end plate 28 secured at the other end of the shaft. Two groups of two magnetic bars 29 and 29a respectively are arranged about the shaft in a manner similar to that of the bars 1'1 and 17a in Figs. 1 and 2. Each of the bars 29 and 29a comprises a main permanently and highly magnetized portion 30 of cobalt steel,or the like, and a reduced portion 31 of mild steel, or similar magnetic material of low magnetic retentivity. Reduced portions 32 of the main portion 30 are fitted into recesses 33in the plate 27. Reduced portions 31 are fitted at one end into recesses 34 in the plate 28, and at the other end into recesses 35 in the ends of the main portions 30. The main portions 30 of the bars 29 are magnetized to present poles 'of like polarity toward the reduced portions 31, and the portions 30 of the bars 29a are magne tized to present poles of like polarity, but opposite to that of the bars 29 presented toward the re Laminated pole-pieces 36 are duced portions 31. provided with openings 36a arranged on the reduced portions 31 of the bars to yoke the bars together in a common magnetic, circuit and reinforce the construction. The laminations are compressed between the plate 28 and a non-magnetic reinforcing disc 37 secured on the reduced portions 31 against a shoulder 38 formed by the .main portion 30, washers 39 being;provided bedepending upon the total magnetic flux desired,

the cross-section of each magnet being limited only by the uniformity of magnetic structure re- .of very low inertia.

' vided a dynamo-electric machine of the magneto type which is of simple, rugged and compact construction, and which employs a rotatable member While 1 have shown and described my invention in connection with a magneto generator of a speciflc type, it will be understood that it is applicable to other types of dynamo-electric machines, and I do not desire my invention to be limited to the specific construction shown and described, and I I intend in the appended claims to cover all modiflcations thereof which do not depart from the spirit and scope of my invention. v

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A rotatable member for dynamo-electric machines comprising a non-magnetic shaft, a magnetic plate secured to said shaft, bars secured to said plate and extending longitudinally along said shaft and spaced circumferentially about said shaft, said bars having permanently and highly magnetized portions at the ends ad- Jacent said plate and portions of low magnetic retentivity at the ends remote from said plate, and pole-pieces secured about said portions of low retentivity. I

2. A rotatable member for dynamo-electric machines comprising a non-magnetic shaft, a nonmagnetic plate secured on said shaft, a magnetic plate secured on said shaft and spaced from said non-magnetic plate, a plurality of magnetic bars arranged longitudinally of said shaft 'between said plates, said bars being arranged in groups spaced circumferentially about said shaft,

each of said bars having a portion of reduced cross-section extending from said non-magnetic plate substantially to the mid-portion of said bar, said portions of reduced cross-section being constructed of a material having a lower magnetic retentivity than the remaining portions of said bars, each of said bars in each of said groups 3 being magnetized in the same direction, adiacent groups of said bars being magnetized in opposite directions, and laminated pole-pieces secured on said reduced portions of the bars of each of said groups.

3. A rotatable member for dynamo-electric machines including a non-magnetic plate, a magnetic plate spaced from said non-magnetic. plate,

a plurality of bars arranged longitudinally between said plates, said bars having permanently and highly magnetized portions at the ends adjacent said magnetic plate and portions of low retentivity at the ends adjacent said non-magnetic plate, said bars being arranged in groups spaced circumferentially about said plates,'each v of said bars in each of said groups being magnetized in the same direction, adjacent groups oi. said bars being magnetized in opposite directions and pole pieces secured toea'ch of said 1 groups of bars near the ends thereof adjacent said non-magnetic plate.

4. A rotatable member for dynamo-electric machines including a magnetic plate, a plurality of bars extending longitudinally and at right angles to said plate and arranged circumferentially about the same, said bars having permanently and highly magnetized portions at the ends adjacent saidplate and portions of low magnetic retentivity at the ends remote from said plate, pole pieces secured about said portions of low retentivity, and a non-magnetic reinforcing plate secured about said bars adjacent the juncture between said highly magnetized por tions and said portions of low retentivity.

LEQNARD' GRIFFI'I'HS.

fiso' 

